In a turbomachine, basically, an energy transfer between a flowing fluid, for example saturated vapor, and the turbomachine itself takes place. In a turbomachine designed as a turbine, the energy transfer is carried out, for example, by means of guide vanes which are profiled in such a manner that by the flow flowing around the guide vanes, a pressure difference between front and back sides occurs and thereby effects the rotation of the guide vanes. Turbines are normally composed of a rotating part, the so-called rotor, and a stationary part, the so-called stator. In the latter, the supply of the working medium to the rotor and a potentially required change of state of the working medium takes place before the medium is guided through the rotor. The working medium transfers a large portion of its energy to the rotor from where the energy is output via a shaft. The housing of the turbomachine normally assumes the function of leading the working medium to the stator as well as of discharging the working medium from the rotor out of the turbomachine.
In some operating states it is desired that the turbomachine, for example the turbine, is not to be acted on with working medium or with a lower mass flow than the available mass flow. In order to achieve this, so-called bypass channels are known from the prior art, which bypass the turbine of the turbomachine and branch off from a feed channel upstream of the turbine and end in said feed channel again downstream of the turbine. Such turbomachines are also used in connection with internal combustion engines in motor vehicles, for example for power generation, wherein in this case, they are integrated in a so-called Rankine cycle in which a working medium such as, e.g., water, ethanol or another organic medium or mixture of different media in liquid and vaporous aggregate states is used.
A method for utilizing waste heat from an internal combustion engine for generating electricity using such a Rankine cycle is known from DE 10 2007 016 557 A1, for example. Here, the working medium is first driven so as to form a circular flow, wherein, at the same time, heat is transferred from an exhaust gas flow of the internal combustion engine to the working medium. Thereby, the heat transfer effects evaporation of the working medium, wherein the saturated vapor, that is, the saturated vaporous working medium is subsequently fed to the expansion machine, thus to the turbine. In the expansion machine, the working medium is relaxed from its overheated state and thereby releases energy, and changes subsequently in a condenser into a liquid aggregate state. In liquid form, it is subsequently brought to a higher pressure level by a pump that is integrated in the Rankine cycle, and is evaporated in the exhaust gas heat exchanger integrated in the exhaust gas flow.
However, the disadvantage of the method known from the prior art is that in particular during a starting phase, it is not necessarily possible to prevent that the working fluid reaches the turbine in still liquid form and causes damage therein, for example by erosion due to droplet impingement.